1. Field of the Invention
The present invention relates to pH sensors and pH measurement methods, and in particular to pH sensors and pH measurement methods suitable for measuring the pHs of solutions of small amounts.
2. Description of the Background Art
A conventional sensor for measuring the pH of a solution employs an ion-sensitive field effect transistor (ISFET). This sensor includes an ISFET 201 and a reference electrode 202, as shown in FIG. 10. To measure the pH of a solution 203, ISFET 201 and reference electrode 202 are placed in sample solution 203. The gate potential of ISFET 201 varies with the pH of solution 203, and such variation is used to measure the pH of the solution. In this conventional technique, however, an ISFET and a reference electrode both must be placed in a solution and for a small amount of solution its pH can hardly be measured.
An object of the present invention is to provide a pH sensor capable of readily measuring the pH of a solution of a small amount.
Another object of the present invention is to provide a pH sensor having a simple structure applicable to biosensors and the like.
According to the present invention, a pH sensor is provided which includes a semiconductor substrate, an insulating film provided on the semiconductor substrate, a solution storage part provided to hold a solution on the insulating film, and a metal electrode provided to be in contact with the solution.
According to the present invention, the solution storage part may have a surrounding wall provided to hold a solution on the insulating film.
According to the present invention, a pH measurement method is provided in which a solution is introduced into the solution storage part of the pH sensor of the present invention as described above, and then a capacitance-voltage characteristic is determined between the metal electrode in contact with the solution and a surface of the substrate forming the sensor which is opposite to the substrate surface having the insulating film provided thereon. A flat band voltage is obtained based on the determination, and the pH of the solution is obtained based on the flat band voltage.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.